1. Field of the Invention
This invention relates to electromagnetic fuel injection valves, and more particularly it is concerned with an electromagnetic fuel injection valve suitable for use with an internal combustion engine.
2. Description of the Prior Art
An electronic fuel injection system generally includes an electromagnetic fuel injection valve built in a suction section of each cylinder of the engine, and a fuel pressurized to a predetermined level is fed to each fuel injection valve. In operation, a current of a pulse duration commensurate with the volume of air intake is passed to the injection valves to open same to allow the fuel to be injected therethrough during the corresponding period of time.
Needle valves are used in the majority of the electromagnetic injection valves of the prior art. To obtain complete fuel cutoff while the injection valves in the form of needle valves are closed requires movement of the needle valves with the axis of each valve being accurately in alignment with the axis of the associated valve seat. To this end, it has hitherto been customary to use needle valves of an increased length to enable the needle valves to be guided at axially spaced-apart two points by guide means. This type of needle valves and guide means require high precision finishes, causing the fuel injection valves to become expensive and the weight of the needle valves to be increased.
In order to reduce the cost of fuel injection systems, there is nowadays a tendency to adopt, instead of the system in which one fuel injection valve is mounted in each cylinder of the engine, a single injection system in which only one injection valve is used and a mixture of air with the injected fuel is distributed to all the cylinders through a manifold. In the single injection system, it is necessary to obtain fuel injection in synchronism with the feeding of air to all the cylinders by using one electromagnetic valve. This makes it necessary for the fuel injection valve to operate at higher speed than fuel injection valves of the system in which one fuel injection valve is provided to each cylinder. Electromagnetic valves of the prior art have found to be handicapped in meeting the requirements of operating at higher speeds because of their heavy weight.
A fuel injection valve in the form of a ball valve is known as from U.S. Pat. No. 3,731,880. This U.S. patent discloses a fuel injection valve including a spring biased magnetic ball which oscillates with respect to a conical valve seat, to open the valve by the attracting force of an electromagnet. In this type of fuel injection valve, the ball itself cooperates with the electromagnetic to constitute a magnetic circuit. Because of this arrangement, the ball would have a large amount of leakage flux, making it impossible to obtain a high attracting force. The result of this would be that the ball could not be forced against the conical valve seat with enough force to prevent imperfect sealing.
SUMMARY OF THE INVENTION
Accordingly, a main object of this invention is to provide an electromagnetic fuel injection valve having a movable valve part of reduced weight suitable to obtain high-speed operation of the valve while eliminating the need to provide high precision finishes as required in electromagnetic fuel injection valves of the prior art.
Another object is to provide an electromagnetic fuel injection valve in which stable operation of the movable parts is ensured in addition to the provision of positive seal to the valve.
Additional and other objects, features and advantages of the invention will become apparent from the description set forth hereinafter when considered in conjunction with the accompanying drawings.